JP5173834B2 - Method and apparatus for sealing a canister loaded with spent nuclear fuel in a cooling bath - Google Patents

Abstract

The process comprises immersing a case (12) and container (10) assembly in a pool, filling the case with nuclear fuel (4) and fitting a cover (D) with a case end plug over the assembly. The pneumatic fluid pressure inside the cover is maintained to hold the water below the level of the container's open end (30) while the open end of the case is closed and sealed using remote-controlled arms (16, 16'), with the seal verified before removing the cover.

Description

  The present invention relates to a method for loading spent nuclear fuel into a cooling bath for temporary storage or reprocessing and even deep site storage, and an apparatus for sealing a canister containing spent nuclear fuel in a cooling bath. And about.

Part of the processing of spent fuel after use in a nuclear reactor includes the step of cooling the spent fuel in a building called a fuel building that is usually located next to the reactor building.
Upon completion of this cooling step, spent fuel is removed from the cooling bath and then stored in a temporary storage location until disposal by either reprocessing or geological storage.
The cooling step in the cooling tank is time limited due to the reduction of the cooling tank capacity.

  In the text, it is assumed that the canister forming the first containment barrier is filled with spent fuel, where each canister itself forms a second containment barrier and imparts mechanical strength to the assembly. Placed in a container. This container is designed to transport the canister to a temporary storage location.

  Currently, spent nuclear fuel is filled in hot cells that provide shielding wall containment and radiation protection. These hot cells have the disadvantage of using heavy and expensive structures.

  Document FR 2806828 discloses an apparatus for sealing spent fuel canisters underwater with a bell jar designed to seal the open end of the canister, where the robot The robot enters the interior of the bell jar through a tube connecting the shape jar to the external environment, and the robot is adapted to attach a cap to the canister.

In the apparatus, a tube for sucking out water inside the canister can be inserted before attaching the cap.
This device and the associated method do not provide a safe packaging of nuclear fuel because no confirmation is made as to whether the canister is sealed. In addition, when the spent fuel is removed from the cooling bath, only one biological protection formed by the canister separates the fuel from the external environment.

  Furthermore, the bell-shaped jar is connected to the external environment, in particular by a welding duct forming a flow path. As a result, it is difficult to achieve sealing of the radiation.

Document DE 8906938 describes a facility for confining nuclear fuel in a canister, which is located in a pool.
The two-part installation includes a lower cylindrical housing in which the canister before being filled with fuel is directly placed, and a bell jar covers the top of the container. At the bottom of the lower housing is a drain for water that has entered the canister.
This storage provides only one biological protection formed by the canister.

Furthermore, this equipment is very large, difficult to handle, and particularly difficult to transport for placement in other cooling tanks.
Further, it is not described whether or not the container can be sealed.
FR 2806828 DE8906938

  Accordingly, it is an object of the present invention to propose a method for containing spent nuclear fuel that can be stored in the atmosphere without risk of exposure.

  Another object of the present invention is to propose an apparatus for safely containing spent nuclear fuel in a cooling bath in a containment that provides dual biological protection.

  Yet another object of the present invention is to propose an apparatus for sealing a canister in a cooling bath that is inexpensive compared to known apparatus.

The above objective is
-Submerge the canister in the container in the cooling bath,
-Attach a sealing device to the top of the container,
-Lower the water level in the sealing device to a position below the open end of the container,
-Attach a cap to the canister,
-Drain water from the canister,
-Achieved by a method of confining nuclear fuel in a cooling bath, comprising the step of checking whether it has been sealed.

The device according to the invention comprises a bell-shaped jar that can cover the container holding the canister, wherein the bell-shaped jar is fitted with a cap, drained from the canister and dried, and there is no water in the canister And means for confirming that the cap is sealed with a cap.
The bell-shaped jar is housed in a cooling bath and placed above the container so as to cover the container when filled with nuclear fuel.

The device of the present invention has the advantage of being easily transportable. In this apparatus, the fuel can be directly contained in the temporary storage cooling tank, and a heavy means such as a hot cell is not necessary. Thus, the operating cost of these devices is reduced.
In addition, direct filling in the cooling bath provides the advantage that biological protection with water is provided and avoids spent fuel being transported without fully safe biological and mechanical protection .
The bell jar is equipped with equipment that allows drying of the fuel element, welding of the sealed cover to the canister, and sealing confirmation. All of these can be remotely controlled and performed underwater.

Therefore, the subject of the present invention is
-Submerge the container and canister in the cooling bath,
-Loading the canister with nuclear fuel,
Adapting the device for sealing the upper end of the container to a canister, wherein the device comprises at least a first canister cap;
-Maintain the air pressure in the apparatus so that the water level is lower than the open end of the packing,
-A cap is attached to the open end of the canister by means within the device;
-Draining water from the canister by means of discharge in the device;
-Confirm the seal provided by the cap;
A method of filling nuclear fuel in a cooling tank in a canister housed in a container, comprising the step of removing the device.

When water is drained from the canister, the water is drained by the pump means, and then gas is sent into the canister to dry the inside of the canister.
After draining the water, for example, it is preferable to perform measurement confirmation of the pressure rise.

Check for sealing
-Send helium into the canister, pressurize the canister with helium,
Detecting helium leakage using a helium spectrometer.

Preferably, the first cap is attached by welding.
The second cap housed in the sealing device is advantageously attached to the first cap before removing the sealing device, where the sealing device may comprise holding means.
It is also possible to put a cap on the jar after the sealing device has been pulled out.

  It is highly preferred that the filling body and the sealing device are arranged in a predetermined position relative to each other, in particular so that confinement can be automated.

  The subject of the invention is also a device for sealing a canister placed inside a container in a cooling bath, wherein the canister is loaded with spent fuel, the device comprising a bell jar, At least one first cap with a connector, means for attaching the cap to the canister, means for attaching the cap to the canister, means for draining, means for confirming complete drainage, and means for controlling sealing of the canister with the cap Prepare.

The sealing device may include an arm that forms a means for attaching a cap to the canister.
The draining means may comprise a pump and means for feeding gas into the canister and drying the canister, wherein the pump and the feed-in means may be connected by at least one connector.
Preferably, the seal verification means comprises means for injecting helium into the canister and a helium spectrometer; the helium injection means may be connected to at least one connector.

The attachment means are advantageously welding means, where these means are brought close to the canister by means of an arm in the bell jar.
Advantageously, the sealing device may include a device for storing a plurality of first caps so that the plurality of canisters can be confined without lifting the sealing device.
The sealing device may also include a device for storing a plurality of second caps designed to be attached to the first cap.
The invention will be more clearly understood from reading the following description and viewing the accompanying drawings.

DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS FIGS. 1A and 1B show a water filled cooling bath 2 that is stored such that spent nuclear fuel 4 is cooled. These fuels may be in the form of a plurality of fuel rods or fuel plates or other shaped assemblies.
This cooling tank can accommodate the sealing device D according to the present invention which can be submerged in the cooling tank even when not in use.

The cooling tank 2 includes a bottom surface 6 on which a base 8 that holds a container 10 in which a canister 12 is disposed is disposed. The canister 12 is designed to contain spent fuel and forms a first containment barrier, where the container 10 itself forms a second containment barrier and is mechanically resistant to the assembly. Is granted.
Container 10 is designed to provide biological containment and its mechanical protection during transport to a temporary storage location.
In the following description, the assembly of the container 10 and the canister 12 is referred to as a filler and is indicated by reference numeral 11.

The method according to the invention is shown in block diagram form in FIG.
-In step 100, the canister 12 sinks the container 10 already placed inside;
-In step 200, the device D is placed above the filling body so as to cover the filling body, where the lower end 28 of the device rests on the base 8 at the bottom of the cooling bath (Fig. 3),
-In step 400, keep the water level at a lower height than the open end 30 of the filler 11,
-In step 500, the cap is fitted and securely attached to the canister, where the sealing device has means to remove water in the canister, to dry the inside of the canister and to ensure that it is sealed to help prevent leakage;
-In step 600, drain the water in the canister;
-In step 700, check the canister to make sure there is no water left;
-In step 800, confirm sealing of the canister.

The device D shown in FIG. 3 comprises a U-shaped bell jar 14 with a substantially inverted cross section, which can be moved in a cooling bath so as to be placed above the filling.
The bell jar may be moved by suspending means 15 attached to the top of the bell jar and connected to an overhead crane.
The bell-shaped jar 14 confirms sealing of canisters operating with cap means, means for attaching caps, eg means for attaching them by welding, means for draining water from inside the canister, means for checking that there is no water in the canister, and Means (not shown).

The bell-shaped jar 14 comprises at least one arm for carrying out the means described above, in the example shown two arms 16, 16 '.
In the example shown in FIG. 3, the device according to the invention comprises an arm 16 ′ for mounting the cap and an arm 16 for welding the cap and checking for confinement.

For example, the arms 16, 16 'formed by two elongate members 16.1, 16.1', 16.2, 16.2 'are connected to each other, where one of the members is for example a clamp Holding means (not shown).
The arms 16, 16 ′ may be controlled externally by an operator or may be moved by a computer program without external intervention.
Arm 16 'fits the cap and advantageously fits an air or helium inlet tube and attaches them to the cap connector.

The bell jar 14 advantageously comprises a device for storing a plurality of canister caps. In the example shown in FIG. 3, the device 22 is located on the inner wall of the bell jar 14. By storing in the bell jar 14, it is not necessary to lift the bell jar for each canister containment.
Advantageously, the storage device can store two types of caps, the first type being designed to contact nuclear fuel, the second type comprising means for holding the canister and the outer surface of the first cap Designed to be attached to.
Advantageously, the two types of caps are stored in separate storage devices.

The base 8 includes means for arranging the bell-shaped jar 14 and the filling body 11 at relative positions suitable for the respective loadings of the canister 12.
The base 8 comprises, for example, a housing 24 having an inner diameter approximately equal to the outer diameter of the filler 11 and a disk 26 having an outer diameter approximately equal to the inner diameter of the lower open end 28 of the bell-shaped jar 14, shown here. In this example, the disk 26 and the housing 24 are coaxial.
As a result, when the bell-shaped jar 14 is mounted on the base 8, it is placed in one fixed position, so is the canister. It is therefore possible to automate the containment method since the arrangement of the fillings, in particular the canister and the bell jar, is always the same. That is, the arm can be moved in a straight line using predetermined commands without operator intervention during the containment step.

The specific steps of the method according to the invention will now be described in detail.
In step 100, the filler 11 is submerged and attached to the housing 24 of the base 8.
In step 300, the device D is placed above the filler 11 and the lower end 28 of the bell jar 14 is moved to a position along the circumference of the disk 26 of the base 8. Each filler 11 and bell jar 14 are always in the same relative position.

In step 400, the water level is kept below the open end 30 of the filler 11 by a pressurization system that injects a gas, eg, compressed air, into the bell jar. As a result, the upper end 30 of the filler 11 is still in the air even when placed in the cooling bath, confining the canister 12 in a dry environment while benefiting from the biological protection provided by the water. Can do.
Advantageously, the inside of the bell jar 14 is kept permanently dry by a pressure system in order to minimize possible damage to the contained equipment. Furthermore, the water level when adapted to the packing is maintained by the pressurization system.

In step 500, the first cap is removed from its storage device 22 by the arm 16 and placed over the open end 13 of the canister 12 to fully seal the canister.
The first cap includes a connector that controls drying and allows helium to be injected into the canister. These connectors are of the self-sealing type well known to those skilled in the art. After injecting helium into the canister, the connector ends are welded.

As will be described below, these connectors can check for water in the canister and confirm the seal provided by the cap after the cap is fitted.
The connector can also drain water from the canister by step 600.
This cap is then attached to the canister 12, preferably by welding. The cap may be screwed.
The welding is, for example, tungsten welding (TIG).

In step 600, the water in the canister is removed by pump means connected to the connector end of the cap. In addition to extraction by the pump means, the inside of the canister is dried by, for example, sending air.
You may drain before attaching the cap.
The canister 12 is aligned with the center of the container 10, and the container 10 is aligned with the portion 24.

In step 700, verify that there is no water in the canister, for example by measuring the pressure rise. This measurement consists of placing the canister in a low pressure state and confirming that the low pressure persists.
If the measurement indicates that water remains in the canister, step 600 is repeated, particularly for drying by injecting air. Thereafter, a new confirmation in step 700 is performed.

If the measurement indicates that the canister interior is dry, then step 800 is performed to confirm the seal provided by the cap and weld. For example, the cap connector is used to inject gas, preferably helium, and then the helium spectrometer is checked for helium leaks on the weld.
If a leak is detected, that is, if the weld is defective, step 1300 is executed. In this step 1300, if there are only a few defects, the weld may be repaired. If not, stop the work, remove the bell jar, remove the canister from the filling, and then open to collect the fuel.

If no leak is detected, step 900 is performed and the second cap is removed from the storage device and attached onto the first cap, for example, by welding. The canister can be held by the second cap. In the case of welding, the means used to weld the first cap to the canister may be used.
If the second cap is not attached to the first cap, step 1000 is performed directly (dotted arrow).

In subsequent step 1000, the bell jar is removed.
Then, in step 1100, a cap is attached to the container.
A cover may be fitted over the container when there is a bell jar.
In step 1200, the container with the loaded canister is removed from the cooling bath.

The sealing device according to the invention comprises a bell jar and all the means necessary for carrying out the method described above.
Therefore, the sealing device is:
-Bell-shaped jar,
At least one first cap with a connector;
-An arm for mounting the cap on the canister;
-Means of attaching a cap on the canister;
-Drainage means, for example formed by means of pumps and gas feed means;
-Means for confirming complete drainage by measuring pressure rise; and-means for confirming sealing of the canister by the cap by injecting helium and detecting helium leakage using a helium spectrometer.

The device is therefore completely autonomous and separated from the external environment by being submerged in a cooling bath. There will be no radiation leaks as no equipment is moved between the bell jar and the environment exposed to the atmosphere.
Further, the sealing device may operate according to a predetermined order without human intervention. Conversely, the operator can control each step.
The bell-shaped jar is, for example, 2 meters in diameter and 3 meters in height.

The sealing device according to the invention can advantageously avoid the use of heavy means such as hot cells for filling the spent fuel.
The sealing device according to the present invention has the advantage that it can be transported to different locations, thus reducing costs because it can be used in multiple cooling baths.

Furthermore, the biological protection provided by water can be maintained by filling in the cooling bath.
Furthermore, by using a canister in the container, a first cover without biological protection inside can be used. Therefore, the first cover has a small thickness. Therefore, the height of the canister is reduced, and as a result, the temporary storage device is filled better.

FIGS. 1A and 1B illustrate an environment for implementing the apparatus and method according to the present invention in a stop mode and a confinement mode, respectively. FIG. 2 is a diagram of the various steps of the method according to the invention. FIG. 3 is a longitudinal sectional view of a loading device according to the present invention.

Claims (17)

A method for sealing a canister (12) contained in a container (10) in a cooling bath (2) :
a) The filling body (11) composed of the container (10) and the canister (12) is submerged in the cooling bath (2),
b) The canister (12) is loaded with nuclear fuel (4),
c) fitting a device (D) for sealing the canister (12) to the upper end of the container (10), wherein the device comprises at least one first canister cap;
d) maintaining the atmospheric pressure in the sealing device so as to keep the water level lower than the open end (30) of the filler (11);
e) A cap is attached to the open end (13) of the canister (12) by means contained within the sealing device (D),
f) Drain water from the canister (12) by means of draining in the device,
g) confirm the seal provided by the cap;
h) A method comprising the step of removing the sealing device (D). When removing the water from the canister (12), after draining by a pump means, to dry the inner canister by feeding a gas to the canister (12), The method of claim 1.   The method according to claim 1 or 2, wherein after draining water, it is confirmed that there is no water in the canister (12).   4. A method according to claim 3, wherein the absence of water is confirmed by measuring the pressure rise. Confirmation of sealed containment
-Send helium into the canister, pressurize the canister with helium,
5. A method according to any one of the preceding claims, comprising detecting helium leaks using a helium spectrometer.   The method according to claim 1, wherein the first cap is attached by welding. A second cap contained in the sealing device, attached to the first cap prior to removal of the sealing device (D), A method according to any one of claims 1 to 6.   The method according to any of the preceding claims, wherein a cap is mounted on the container (10) after removing the sealing device (D). 9. The method according to claim 1 , wherein during step c) the filling body (11) and the sealing device (D) are arranged in a predetermined relative position with respect to each other.   A device for sealing a canister (12) accommodated in a container (10) in a cooling tank, wherein the canister (12) is loaded with spent fuel and the water level is loaded with the canister (12). A bell-shaped jar (14) designed to cover the open end of the container, with means capable of maintaining the pressure in the bell-shaped jar to be kept lower than the open end (30) of the container Wherein the bell jar is designed to receive at least one first cap with a connector, wherein the bell jar also includes means (16) for attaching the cap to the canister (12). ), A device comprising means for mounting the cap on the canister, drainage means, means for confirming complete drainage, and means for confirming sealing of the canister with the cap   The apparatus of claim 10, comprising an arm forming means for attaching the cap. The drainage means comprises a pump and means for feeding gas into the canister (12) to dry the canister, wherein the pump and the means for feeding are connected to at least one of the connectors of the first cap. 12. A device according to claim 10 or 11, which is good.   13. Apparatus according to any of claims 10 to 12, wherein the seal verification means comprises means for injecting helium into the canister (12) and a helium spectrometer.   The apparatus of claim 13, wherein the helium injection means is connected to at least one connector.   15. A device according to any of claims 10 to 14, wherein the attachment means are welding means, wherein these means are brought close to the canister by means of an arm in the bell jar.   16. A device according to any of claims 10 to 15, comprising a device for storing a plurality of first canister (12) caps. Having a device for storing a plurality of second caps designed to be attached to the first cap, according to any of claims 10 to 16.

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